Evolution and decay of a stable and a dynamic airglow patch

Abstract

This study investigates the evolution of two polar cap airglow patches, AGP1 and AGP2, observed over Resolute Bay in northern Canada. AGP1 exhibited stable shape, followed the ExB drift patterns and maintained high electron density as it transited toward the auroral oval, sustaining the maximum F-region density and redline emissions by a downward vertical drift. An initial non-uniform density decay was observed in AGP1’s density profile; the topside shifted downwards, resulting in increased bottomside density. Later, the maximum and bottomside density started to decay. Overall, the downflow contributed to a faster density decay. In contrast, AGP2 displayed dynamic characteristics, halting its motion mid-polar cap, followed by a prolonged decay in both electron density and redline emission. Observations and GEMINI simulations revealed that recombination between atomic ions and neutral molecules was the dominant mechanism for density decay in the optical layer. The decay rate was affected by vertical drift, magnetic field line orientation, and local neutral atmosphere conditions, which may be influenced by prior patch activity. Simulations of AGP1 using GEMINI and GLOW highlight the importance of vertical ExB drift in sustaining electron density maximum and redline emission intensity. By using various free parameters in the model to tune our simulations (e.g. background precipitation) we are able to achieve reasonable agreement with observed patch behavior. Our findings emphasize the interplay between vertical drift, recombination rates, and neutral wind in determining polar cap patch evolution, as well as the complexity of patch dynamics and their dependence on local ionospheric and atmospheric conditions.